The present invention relates to a method and device for producing a fuel containing carbon. Such fuels can be used, for example, for converting raw materials containing carbon into preferably liquid fuels. In this context, it has been known for a long time from the prior art to gasify biomass in order to obtain fuels in this manner. Thus, for example, a method for gasifying biomass and a plant for this are known from DE 102 27 074 A1. In this, the substances are burned in a combustion chamber separated in a gas-tight manner from a gasification reactor, and the thermal energy from the combustion chamber is introduced into the gasification reactor.
It is known in the prior art that renewable raw materials, such as wood, straw, hay and oil-containing plants, can be used as a substitute for fossil energy carriers, such as fuel oil and natural gas. In addition, refuse and waste also generally are increasingly being discovered as secondary raw materials and are being put to thermal utilization.
EP 1837390 A1 discloses a method and a device for processing untreated wood and similar fuel. In this method, this fuel passes through a drying phase and can then be provided for production of heat. In this context, the purely biological fuel is processed with the addition of quicklime and this mixture is used for production of heat directly or after a compaction which follows the mixing. A reduction in the water content in the fuel is said to be achieved by the addition of quicklime.
This is known, for example, for sewage sludges, which because of worldwide restrictive directives are being used increasingly as a raw material for thermal gasification. However, conventional primary raw material carriers, such as coal, are also acquiring an importance as energy carriers which will increase in the future. The conversion of fuels containing carbon into thermal energy can take place directly or can also be used for production of higher performance fuels or also gas or bio fuels.
Processes known in this respect are fermentation, combustion, oil conversion and gasification of such fuels. In this context it is likewise known to carry out thermal conversions of such fuels in a high temperature range from approx. 800° C. In order to carry out this conversion, the raw materials should have a low moisture content. It is known in this context to comminute, such as, for example, to chop, shred, mince, the raw materials before use and then to dry and to press them and to feed them to the conversion process in compressed form. In this context, in the prior art pressing of the raw material is carried out, for example, with hydraulic or mechanical presses, which leads to an easier handling for the subsequent processing process.
In the actual thermal conversion processes, such as, for example, a combustion or gasification, however, in the prior art a formation of lumps, reduction to slag or vitrification of the ash may occur, which in turn causes increased difficulties in the cleaning of corresponding plants. It is therefore known from the prior art that lime or dolomite is added to the fuel in order to achieve an increase in the ash melting point or ash softening point in this manner.
Some biomasses, such as, for example, straw, thus have a high chloride or potassium content, their ash softening point of about 800° C. being significantly below that of, for example, wood of 1,200° C. In the case of pressed articles of forest wood and residual wood also, an addition of lime increases the ash melting point or the ash softening point and in this manner allows a use of the pressed fuel articles at temperatures in the thermal conversion process of more than 1,200° C. This also applies correspondingly to pressed articles produced from waste and sewage sludges with a high mineral content.
It is furthermore known from the prior art to mix the raw material with the additive, for example pulverulent lime, beforehand and then to compress the mixture. However, this results in disadvantages during the compressing operation, that is to say the strength of the pressed articles is impaired by this operation.